Structural Biology Program, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA.
Structure. 2011 Jun 8;19(6):821-32. doi: 10.1016/j.str.2011.03.020.
DNA is susceptible to alkylation damage by a number of environmental agents that modify the Watson-Crick edge of the bases. Such lesions, if not repaired, may be bypassed by Y-family DNA polymerases. The bypass polymerase Dpo4 is strongly inhibited by 1-methylguanine (m1G) and 3-methylcytosine (m3C), with nucleotide incorporation opposite these lesions being predominantly mutagenic. Further, extension after insertion of both correct and incorrect bases, introduces additional base substitution and deletion errors. Crystal structures of the Dpo4 ternary extension complexes with correct and mismatched 3'-terminal primer bases opposite the lesions reveal that both m1G and m3C remain positioned within the DNA template/primer helix. However, both correct and incorrect pairing partners exhibit pronounced primer terminal nucleotide distortion, being primarily evicted from the DNA helix when opposite m1G or misaligned when pairing with m3C. Our studies provide insights into mechanisms related to hindered and mutagenic bypass of methylated lesions and models associated with damage recognition by repair demethylases.
DNA 容易受到许多环境因素的烷基化损伤，这些因素会改变碱基的沃森-克里克边缘。如果这些损伤得不到修复，可能会被 Y 家族 DNA 聚合酶绕过。旁路聚合酶 Dpo4 被 1-甲基鸟嘌呤（m1G）和 3-甲基胞嘧啶（m3C）强烈抑制，在这些损伤处掺入核苷酸主要是诱变的。此外，在插入正确和不正确的碱基后进行延伸，会引入额外的碱基替换和缺失错误。Dpo4 与正确和错配的 3'-末端引物碱基相对的损伤的三元延伸复合物的晶体结构表明，m1G 和 m3C 都仍然位于 DNA 模板/引物螺旋内。然而，正确和不正确的配对伙伴都表现出明显的引物末端核苷酸扭曲，当与 m1G 相对时，主要被逐出 DNA 螺旋，而与 m3C 错配时则不对齐。我们的研究提供了对与甲基化损伤的受阻和诱变旁路以及与修复去甲基酶相关的损伤识别相关的机制的深入了解。
